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Glycosyl imidates, 69. Synthesis of flavoneC-glycosides vitexin, isovitexin, and isoembigenin

✍ Scribed by Mahling, Jürgen-Andreas ;Jung, Karl-Heinz ;Schmidt, Richard R.

Publisher: John Wiley and Sons
Year: 1995
Tongue: English
Weight: 727 KB
Volume: 1995
Category: Article
ISSN: 0947-3440
DOI: 10.1002/jlac.199519950362

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✦ Synopsis

Abstract

2‐Hydroxy‐4,6‐dimethoxyacetophenone (4) was glycosylated with O‐(2,3,4,6‐tetra‐O‐benzyl‐α‐D‐glucopyranosyl) trichloroacetimidate (5) and trimethylsilyl triflate as promoter to yield directly the C‐glycoside 6. Construction of the flavone system by application of a Baker‐Venkataraman‐type rearrangement followed by deprotection yielded isoembigenin (2). Glycosylation of 4,6‐bis(tert‐butyldimethylsilyloxy)‐2‐hydroxyacetophenone (17) with the trichloroacetimidate 5 afforded the O‐glycoside intermediate 18 which was converted via Fries rearrangement into the C‐glycoside 21. Applying again the Baker‐Venkataraman rearrangement and cyclization gave isovitexin and vitexin derivatives 25 and 26, which were completely deprotected to yield isovitexin (1b) and vitexin (1a), respectively.

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